1. Field of the Invention
The present invention relates to a switch having a switching mechanism that switches in the presence of overtemperature, for opening and closing a circuit that can be connected to external terminals of the switch, the switching mechanism comprising an electrically conductive spring element which, as a function of the temperature of a bimetallic element, operates against the latter and in the idle position is electrically connected to one external terminal, and carries a movable contact which, as a function of the temperature of the bimetallic element, is in contact with a fixed contact that is electrically connected to the other external terminal.
2. Description of Related Art
A temperature-dependent switch of this kind is known from DE 29 17 482 C2.
The known switch serves to monitor the temperature of a device. To this end, it is connected via its external terminals in series with the device being monitored, and is arranged so that the temperature of the device being monitored influences the temperature of the bimetallic element. If the switching temperature is exceeded, the switching mechanism opens the connection between the two external terminals, and the electric circuit passing through it is interrupted. When the temperature drops, the electric circuit is closed again, although this need not absolutely be the case; bistable temperature-dependent switches are also known.
The known switch has a housing consisting of an electrically conductive lower housing part and an electrically conductive cover part which caps the latter, an insulating film being provided for insulation between the lower housing part and cover part. An inwardly projecting region on the cover part is configured as a fixed contact. The switching mechanism has a spring disk on which the movable contact, which comes into contact with the fixed contact, is mounted by means of a crimped rim. A bimetallic snap disk, which below the switching temperature is received unconstrainedly in the housing, is slipped over the spring disk. Current flow occurs via the conductive cover part, the contact, the spring disk, and the conductive lower housing part in which the spring disk is supported. When the switching temperature is exceeded, the bimetallic snap disk snaps over and pushes the spring disk, with its contact, away from the cover part.
Mechanical assembly of the known switch is laborious in particular because the contact must be mounted by means of the crimped rim on the spring disk.
A comparable switch is known from DE 37 10 672 A1. This so-called temperature controller is configured to be self-holding, i.e. it comprises a heating resistor, connected in parallel with a bimetallic switching mechanism, which when the switching mechanism is open is connected in series between the external terminals, and heats up as a result of the current flowing through to the point that it keeps the bimetallic switching mechanism above its switching temperature, so that it does not return back to the original state. The high-ohmic resistor is integrated into the cover part, which consists of either insulating material or an electrically conductive resistor material.
In the case of this switch the movable contact is placed loose into the spring disk, and clamped between the spring disk and the bimetallic snap disk by means of a projecting annular shoulder.
The disadvantage here is that during final assembly, which is generally performed manually by semi-skilled personnel, first the spring disk must be placed into the lower housing part, then the contact part into the spring disk, and lastly the bimetallic snap disk must be placed over the contact part. This procedure is very time-consuming, and admits of only limited automation. Moreover it can cause the contact part to slide during assembly, thus increasing rejects.
In order to eliminate these disadvantages, it has already been proposed, in DE 43 37 141 A1, to weld the contact onto the spring disk.
Although this eliminates the aforementioned disadvantages in terms of final assembly of the switch, it is still necessary, as in the case of the switch from DE 29 17 482 C2 mentioned earlier, to mount the contact onto the spring disk by means of additional actions.
In all the known switches discussed so far, the movable contact is a part to be turned that can be manufactured only with corresponding material and production outlay, so that it contributes significantly to the total cost of the known switch.